Adhesive-faced porous absorbent sheet and method of making same

ABSTRACT

A sheet-form material suitable as wound dressing and having enhanced moisture control properties is disclosed. This sheet-form material includes a porous sheet of absorbent, elastomeric segmented polyurethane having an open pore structure and an apertured adhesive facing on one side of the porous sheet. A liquid impermeable but water vapor permeable backing may be provided on the opposite side of the porous sheet, if desired. Also disclosed is a method for forming an apertured adhesive facing for the sheet-form material.

This is a division of application Ser. No. 07/150,539, filed Feb. 1,1988, now U.S. Pat. No. 4,906,240.

TECHNICAL FIELD

This invention relates to an absorbent sheet and in particular to apolyurethane absorbent sheet suitable as a wound dressing.

BACKGROUND OF THE INVENTION

Wounds produce exudate. The composition of this exudate varies dependingupon the nature and location of the wound. While an exudate can begenerically characterized as an aqueous mixture of proteinaceousmaterials, it may also contain blood components, etc., and may serve asa growth medium for bacteria.

In clinical practice, the dressing of wounds has traditionally beenaccomplished by cleansing the injured area and covering it withabsorptive, gauze type materials. In this way the wound is kept "cleanand dry" throughout the duration of its healing process.

However, there has been increasing acceptance of the view that foroptimal wound healing to occur from the standpoint of rate of healing,quality of healing, etc., a moist microenvironment around the wound ispreferential as opposed to the "clean and dry" approach. As thisacceptance of the moist wound healing theory has grown, wound dressingspromoting a moist wound microenvironment have entered the marketplace.

The control of exudate is of prime importance if a moist woundmicroenvironment is to be maintained. It can be appreciated that if adressing removes all the exudate that a wound produces, a "dry" woundresults which is suboptimal for wound healing. Similarly, if thedressing does not control the level of exudate sufficiently, then anexcess "pool" of material develops which may subsequently leak thussoiling clothing and bed linen, and breaching any barrier to bacterialinfection.

Ideally, a wound dressing must be adhesive in nature such that it mayattach to the wound site. The adhesive utilized must be biocompatible,non-cytotoxic and free of toxic leachable substances as well as have thedesired balance of physical properties such as moisture vapor transportrate, tack, long term adhesion properties, etc. Inasmuch as in use theadhesive will be in direct contact with the wound site and surroundingintact area, it must be non-toxic and should elicit no more than aminimal allergenic response.

Additionally, a wound dressing should possess the ability to preventbacteria from entering the wound from the ambient environment whileproviding the proper moisture vapor transport rate.

Other aspects such as a dressing's ability to conform to irregularcontours of the body are also desirable. This may be accomplished byutilizing elastomeric, flexible, polymeric materials in the constructionof the dressing.

Having outlined the major desirable design characteristics ofenvironmental wound dressings it is beneficial to examine the mode ofoperation of existing wound dressings to appreciate their deficiencies.

Environmental dressings, i.e., dressings which maintain a beneficialmicroenvironment around a wound, can be categorized into three broadclasses: hydrocolloid/gel dressings; film dressings; and foam dressings.

These dressings maintain specific microenvironments, e.g., moisture,temperature, gaseous transport, etc., around a wound by utilizing avariety of physical mechanisms.

Hydrocolloid type dressings as described in U.S. Pat. No. 4,477,325 toOsburn are relatively thick and as a result possess low conformability.The mode of exudate control is by absolute absorption by a gel(hydrocolloid) in the dressing. The ability for moisture to pass throughthe dressing to the external environment is minimal. On highly exudingwounds the dressing's absorption capacity can be exceeded which leads toleakage and subsequent disruption of the bacterial barrier. Somehydrocolloid compositions dissolve and fall into the wound bed thusrequiring time consuming cleaning, which disrupts the wound site, atsubsequent dressing changes.

The ability of a film dressing to transport moisture is a function offilm thickness and chemical composition. On moderate to high exudingwounds, exudate tends to collect under film dressings and form "pools".This collection of exudate indicates that current polymer film dressingshave a moisture vapor transmission rate which is too low to handle theexudate from many wounds. It has been suggested that the "pool" ofexudate may increase the risk of bacterial proliferation leading toinfection. Similarly, if the "pool" reaches excessive proportionsleakage will occur thus breaking the bacterial barrier.

Polymer film dressings as described in U.S. Pat. No. 3,645,835 toHodgson and U.S. Pat. No. 4,513,739 to Johns are thin and possess highconformability. The wound contacting surfaces are coated with pressuresensitive adhesives carried on the film. The films that are used areliquid impermeable polyurethane elastomers. Thus wound exudate is notallowed to ingress into the film. The sole mode of exudate control is byallowing vapor of the aqueous portion of the exudate to permeate intothe polymer film from where it diffuses into the external environment.As the moisture vapor permeability is low, the polymer film's absoluteabsorption capacity is also low especially when compared to hydrocolloiddressings.

Foam dressings also manage exudate by evaporation of the aqueous portionof the exudate through the dressing to the surrounding environment.Control of this moisture vapor transmission rate is a function of thechemical composition of the foam coupled with the pore structure. Due totheir gross pore sizes, foam dressings tend to desiccate woundsresulting in dressings which become brittle and nonconformable duringuse. These hardened dressings often traumatize the underlying healingwound bed. Furthermore, either special processing and/or a wetting agentis required to make the foam hydrophilic.

Dependent upon the type of foam structure used, exudate is also managedby capillary action into the pores of the structure. Most foamstructures used as dressings contain interconnecting pores and thusprovide limited bacterial barrier properties because the mean porediameter exceeds the dimensions of many bacteria. Similarly, suchdressings contain pore sizes which are sufficiently large as to fallinto the range of sizes into which regenerating tissue will grow. As aresult of this, ingrowth of tissue into the dressing's structure occursthus impeding removal of the dressing and traumatizing the wound site.

Open cell foam dressings are described in U.S. Pat. No. 3,975,567 toLock and U.S. Pat. No. 3,978,855 to McRae et al. The foam is madehydrophilic by permanently compressing the cells of the microporous foamto form a microporous skin which contacts the wound site. Thus thesepatents teach against larger pores contacting the wound site and smallerpores away from the wound site as is taught by the present invention.Also, a wetting agent is added to enhance absorption of exudate into theporous structure.

An example of a foam dressing with pores into which regenerating tissuegrows is U.S. Pat. No. 3,949,742 to Nowakowski. In this particularinvention a thrombogenic open cell reticulated foam is used laminated toa non-porous polyurethane film. The dressing provides a matrix intowhich fibroblasts and new capillaries can grow. Thus the wound site istraumatized by removal of the dressing.

The present invention maintains the desired level of moisture,temperature and gaseous exchange at the wound site. By the control ofthese properties, the microenvironment thus produced is the optimalrequired for healing of the wound. At the same time, the presentinvention manages exudate, is adhesive, biocompatible, non-toxic,conformable, elastomeric and also provides a bacterial barrier.

SUMMARY OF THE INVENTION

The present invention contemplates an adhesive-faced absorbent sheetwell suited for making a wound dressing which enhances the healing of awound by providing about the wound a microenvironment that promoteshealing. A method of manufacturing the absorbent sheet is alsocontemplated.

The adhesive-faced sheet of this invention is an absorbent, elastomeric,porous polyurethane sheet provided with an apertured adhesive facing onone side of the porous sheet. For use as a wound dressing, an optionalpolyurethane sheet or film may be provided as a backing for the porouspolyurethane sheet. The polyurethane preferably is a segmentedpolyurethane.

More particularly, the present wound dressing comprises anadhesive-faced porous sheet of absorbent, elastomeric, polyurethanehaving an open pore structure and defining macropores at one surface ofthe porous sheet. The adhesive facing for the porous sheet is providedcontiguous with the macropore containing surface and defines aperturesthat communicate with the macropore and provide fluid channels to themacropore and thus to the interior of the porous sheet.

The wound dressings of the present invention control exudate andmoisture level at the wound site by controlling the absolute absorptionand moisture vapor transport rate of the exudate. These parameters areadjusted by modifying the chemical composition of the polyurethane usedto make the porous sheet, the porous structure of the sheet, and thecomposition and thickness of the apertured adhesive facing. Thus aseries of wound dressings which provide a continuum of differentmicroenvironments is provided. These dressings can be designed to suitparticular wound types, e.g., ulcers, donor sites, burns, high exudingand low exuding wounds, etc. They are easy to use and maintain thedesired microenvironment to attain optimal wound healing.

A method of forming the wound dressing having an apertured adhesivefacing is also disclosed. According to this method, the porous,elastomeric segmented polyurethane sheet and a viscous sheet-formadhesive layer are juxtaposed, and then the porous polyurethane sheet iscompressed against the adhesive layer for a relatively short timeperiod, e.g., by passing a roller over the surface of the porous sheetopposite from the surface in contact with the adhesive layer. Uponrelease of the applied compressive force, the elastomeric porous sheetsprings back to its previous configuration while generating apertures inthe adhesive layer contiguous therewith. After the foregoing treatment,the adhesive layer remains as an apertured adhesive facing on the porouspolyurethane sheet.

Numerous other advantages and features of the present invention willbecome readily apparent from the following detailed description of theinvention, the accompanying examples, drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary sectional view of an absorbent wound dressingembodying the present invention as applied to a wound site;

FIG. 2 is a sectional view of a method for forming apertures in theadhesive facing of the present wound dressing;

FIG. 3 is a micrograph illustrating macropores on the surface of theporous segmented polyurethane sheet;

FIG. 4 is a micrograph illustrating an adhesive layer as applied to theporous segmented polyurethane sheet but before formation of aperturestherein;

FIG. 5 is a micrograph illustrating the interface between the poroussegmented polyurethane sheet and the adhesive facing contiguoustherewith; and

FIG. 6 is a micrograph illustrating apertures in the adhesive facing ofthe present wound dressing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention is susceptible to embodiment in many differentforms, preferred embodiments of the invention are shown and described inthis specification. It should be understood, however, that the presentdisclosure is to be considered as an exemplification of the principlesof this invention and is not intended to limit the invention to theembodiments illustrated.

As shown in FIG. 1, the wound dressing 10 of the present inventionincludes an absorbent porous sheet or layer 12 which is capable ofabsorbing exudate 44 from a wound bed 28 of a wound site 26. Preferably,micropores as well as macropores are present in sheet 12. In theembodiment shown in FIG. 1, macropores 14 and micropores 15 in theporous sheet 12 provide a pore size gradient 18 of decreasing pore sizeacross the thickness of sheet 12, i.e., from a first or bottom face 20to a second or top face 16. Openings 22 in bottom face 20 are formed bymacropores 14 that extend to the surface of sheet 12. An adhesive layer30 on first face 20 provides an adhesive facing for the wound dressing10. Apertures 24 in the adhesive layer 30 are formed by therepositioning of adhesive portions or fragments 32 of the adhesive layer30 to the interior of macropores 14 as will be described in greaterdetail hereinbelow.

An optional hydrophilic backing layer 34 is provided on the second face16 as a backing for the wound dressing 10. Hydrophilic layer 34 isuseful to further modulate the rate of vapor transmittal through thedressing and thus aids in maintaining the proper moisture content at thewound site 26 during the healing process.

The absorbent microporous layer utilized herein is a biocompatiblehydrophilic polyurethane or the like. Preferred for the present wounddressings are segmented polyurethanes of the type disclosed in U.S. Pat.No. 4,704,130 to Gilding et al and in U.S. Pat. No. 3,635,907 to Schulzeet al. Other suitable materials are polyurethanes derived frompolyethylene glycol linked with glycerol and toluene diisocyanate ormethylene diisocyanate, e.g., the Hypol™ type materials commerciallyavailable from W. R. Grace & Co.

The porous nature and a desired pore size gradient in the absorbentporous layer can be achieved by a controlled precipitation process asdescribed in U.S. Pat. No. 4,704,130 to Gilding et al. Utilizing thatprocess, the structure, pore size distribution and pore size gradient ofthe porous layer can be altered by adjusting any or all of the followingvariables:

(a) Percent polymer in solution--increasing the solids content of thepolymer solution increases the viscosity of the solution and decreasesthe pore size of the resultant porous layer.

(b) Molecular weight of the polymer in solution--increasing themolecular weight of the polymer in solution will decrease the size ofthe pore of the resultant porous layer.

(c) Solvent/non-solvent ratio of the polymer solution--decreasing thesolvating power of the solvent or solvent/non-solvent in which thepolymer is dissolved will result in a porous layer with smaller pores.

(d) Temperature of the polymer solution--increasing the temperature ofthe polymer solution will increase the relative solubility of thepolymer and lead to increased porous layer porosity.

(e) Type of non-solvent in precipitation bath--choice of non-solventswhose solubility parameters indicate that they are almost solvents forpolyurethane will result in a porous layer with larger pores. Use ofnon-solvents whose solubility parameters indicate that they are far frombeing solvents will result in a porous layer with smaller pores.

(f) Solvent/non-solvent ratio in the percipitation bath--as in (e)above, the solubility parameters of the mixture will determine poresize, i.e., if the mixture is close to being a solvent large pores willbe produced and if the mixture is far from being a solvent small poreswill be produced.

(g) Temperature of the precipitation bath --the higher the temperatureof the precipitation bath the more open the pore structure of theresulting porous layer.

(h) The rate of immersion of the polymer solution into the precipitationbath--the faster the immersion, the tighter the pore structure of theresultant porous layer.

The adhesive layer for the adhesive facing of the present wound dressingis compounded to be non-cytotoxic and non-allergenic when used onpatients. The adhesive properties of the facing are selected to give thedesired degree of bioadhesion, tack, etc., while maintaining the desiredlevel of hydrophilicity and moisture transport. The adhesive propertiesof the adhesive layer are adjusted so that the cohesive strength of theadhesive is less than the adhesive strength of the adhesive to theporous sheet, and further so that the adhesive strength vis-a-vis theporous sheet is greater than that vis-a-vis the tissue in contact withthe adhesive. In addition, the elastic modulus of the porous sheet ishigher than the ultimate tensile strength of the adhesive layer. Thecohesive strength of the adhesive also is less than the tensile strengthof the porous sheet. The adhesive facing usually is about 0.0002 toabout 0.001 inches (about 5 to about 25 microns) thick, preferably about0.0005 inches (about 12.5 microns) thick.

Preferably, the adhesive is a visco-elastic, acrylic-based pressuresensitive adhesive constituted by copolymers of 2-ethylhexyl acrylateand acrylic acid having a tensile strength of no more than about 2.5grams per square millimeter at a strain rate of 25 times the samplelength per minute. The amount of acrylic acid present usually is in therange of about 10 to about 25 mol-percent, preferably about 12 to about17 mol-percent.

The acrylic-based pressure sensitive adhesive as a 40 weight percentsolution in ethyl acetate preferably has a viscosity of no more thanabout 15,000 centipoises at about room temperature, more preferably aviscosity in the range of about 500 to about 8,000 centipoises.

Other suitable pressure sensitive adhesive compositions are described inU.S. Pat. No. 3,645,835 to Hodgson.

The outer hydrophilic layer or backing is preferably made from a solventcast polyurethane as a thin film. This film is liquid impermeable butwater vapor permeable. By varying the chemical composition, the moisturevapor transmission rate (MVTR) of the film can be adjusted as desired.Due to the nature of the outer hydrophilic backing, bacterial barrierproperties for the present wound dressings are obtained as well. Thepreferred nominal thickness of this layer is approximately 0.002 inches(0.005 cm).

The present wound dressing is packaged in sterile heat sealable poucheswith the adhesive facing protected by a release sheet. The preferredsterilization method is by gamma irradiation. However, steam autoclavingor ethylene oxide treatment may be utilized.

Although the preferred form of the present wound dressing includes threelayers, as pointed out hereinbefore the backing may be omitted.

A method for producing an apertured adhesive facing is shown in FIG. 2.First, a laminate 38 is produced by juxtaposing porous absorbent sheet12 and adhesive layer 30. Next a force is applied to the laminate 38 soas to compress sheet 12 against adhesive layer 30. While FIG. 2discloses a roller 36 as applying the desired compressive force, otherknown suitable means to achieve compression are acceptable. The appliedforce urges portions of the inner surface of pores 14 in contact withthe adhesive layer 30 through openings 22. Subsequent removal of theapplied force allows the absorbent porous sheet 12 to substantiallyreturn to its pre-compression configuration. However, a portion of theadhesive in contact with the inner surfaces of macropores 14 is retainedthereon, thereby producing apertures or holes 24 in the adhesive facingin registry with macropores 14. The apertures 24, in turn, provide fluidaccess to the interior of sheet 12.

FIGS. 3-6 are scanning electron micrographs at 30× magnification of awound dressing made in the foregoing manner. In particular, FIG. 3 showsan absorbent sheet surface 20 of the porous layer 12 before applicationof the adhesive layer. Openings 22 are defined by macropores that extendto the surface of the porous sheet. FIG. 4 shows the adhesive layer 30as applied to the porous sheet before the latter is compressed. FIG. 5shows the underlying microporous layer 12 and the edge 42 of theadhesive layer 30. Finally, FIG. 6 shows the apertured adhesive facingderived from the applied adhesive layer 30 after application of thecompressive force to the porous layer. The aperture density was about8.6% as measured by computer digitization.

As illustrated in FIGS. 5 and 6, not all of the openings 22 of themicroporous sheet 12 result in apertures 24 in the adhesive layer 30.However, that is not required. For effective exudate transport throughthe adhesive layer 30, minimum aperture surface density in the adhesivefacing can be as low as about 1 to about 2%. The preferred surfaceaperture density in the adhesive facing is about 5 to about 15%. Thesurface aperture density can be as high as about 25%.

While not wishing to be bound by a particular mechanism of operation,the present invention is believed to function as a wound dressing in thefollowing manner.

The dressing is placed onto a wound site with the adhesive side towardthe wound bed. The pressure sensitive adhesive adheres to the intactskin around the wound bed. Similarly, it is believed that the adhesiveadheres initially to the moisture exuding wound bed as well as to thesurrounding region. Over a period of time the adhesive contacting thewound bed may hydrate such that it is no longer firmly adhered to thewound. The dressing, however, is maintained in close apposition to thewound bed by the capillary action of the exudate entering themicroporous substructure of the dressing. Due to the designed level ofmoisture vapor transmission rate (MVTR) and controlled discontinuities,i.e. the apertures, in the adhesive layer, proteinaceous exudate passesinto the porous structure of the absorbent microporous layer of thedressing.

The level of hydrophilicity of the microporous layer and porearchitecture are designed such that surface tension is minimized toallow the easy passage of exudate into the pores. The exudate isretained in the dressing's pore structure while maintaining a highrelative humidity at the wound site. The pore size of the porous sheetof the dressing can be controlled to provide a matrix into whichregenerating tissue cannot grow, if desired.

When a backing is provided over the exudate-retaining sheet of thedressing, further control of the loss of the aqueous portion of theexudate by evaporation is possible. In this manner a balance betweenmoisture loss and exudate uptake may be attained while maintaining amoist wound microenvironment.

The following examples illustrate typical processes and compositions forpracticing the present invention, but are not to be construed aslimitations thereof. In these examples, certain materials are referredto by their commercial names in the interest of brevity. These materialsare:

Mitrathane™ M1020--a segmented polyetherurethane-urea derived fromdiphenylmethane diisocyanate, polytetramethylene glycol having a numberaverage molecular weight of about 1,000, and organic amines in an amountsufficient to provide for about 20-fold chain extension;

Mitrathane™ M2007--a segmented polyetherurethane-urea derived fromdiphenylmethane diisocyanate, polytetramethylene glycol having a numberaverage molecular weight of about 2,000, and organic amines in an amountsufficient to provide for about 7-fold chain extension; and

Mitrathane™ MPU-5--a segmented polyetherurethane-urea derived fromdiphenylmethane diisocyanate, polytetramethylene glycol, polyethyleneglycol, and organic amines as chain extenders.

All of the above materials are commercially available from MatrixMedica, Inc., Wheat Ridge, Colo.

EXAMPLE 1 Manufacture of Absorbent Sheet

The porous layer of the present invention is manufactured from asegmented polyurethane such as Mitrathane™ M1020. The material issupplied as a 25 weight percent solids solution in dimethylacetamide(DMAC). To this Mitrathane™ solution a solution of polyvinylpyrollidone(PVP) (M.W. 360,000) in DMAC is added such that the total solids of themixture is 15 weight percent in DMAC (12% Mitrathane™ M1020; 3% PVP).The resulting viscosity of the produced mixture at 21° C. is within therange of about 1,500-2,500 cp as measured using a Brookfield viscometer.This mixture is cast onto a substrate to a nominal thickness of about0.05 inches. By known methods, such as described in U.S. Pat. No.4,704,130 to Gilding et al., the substrate and cast solution areimmersed in a water bath at about 15° to about 25 ° C. The polymerprecipitates out of solution while in the water bath. The time elapsedin the water bath is between about 5 to about 30 minutes. The poroussheet thus formed is dried, while being constrained, at about 45° toabout 55° C. for about two hours in a forced hot air oven.

The structure of the produced sheet includes one surface with pores inthe range of about 0.1 to about 1 micron as revealed by a scanningelectron microscope (SEM). Under this surface lie "finger-like" voids ormacropores having dimensions of approximately 20 microns across byapproximately 750 microns deep. These voids extend to the other surfaceof the formed sheet and define therein fluid access openings.

The thus formed porous sheet has the following physical properties:tensile strength to break--0.09 kg/mm² ; elongation at break--326%;Moisture Vapor Transmission Rate (MVTR), measured by the modified ASTMTest No. E-96-80 using an inverted cup at 37° C.--25,000 g/m² /24 hrs;water absorption--500%.

EXAMPLE 2 Manufacture of Adhesive Layer

The adhesive is formulated to be hydrophilic and consists essentially ofa biocompatible copolymer of 2-ethylhexyl acrylate and acrylic acidcontaining about 15 mol-% of the latter. It is supplied as a 40% solidssolution in ethyl acetate. The solution of adhesive is spread onto arelease paper to obtain a uniform coating. The release paper andadhesive layer are placed in a forced hot air oven at approximately 45to approximately 55° C. for about 2 hours to remove residual solvent.The adhesive layer is cast such that a final adhesive coating weight ofapproximately 12 g/m² is obtained.

EXAMPLE 3 Manufacture of Backing Sheet

The outer polyurethane layer is prepared from a polyurethane such asMitrathane™ MPU-5. The material is supplied as a 25 weight percentsolids solution in dimethylacetamide (DMAC). This solution is spread tothe desired thickness on a glass plate and the solvent removed byheating to a temperature in the range of about 50° to about 70° C. forapproximately 2 hours.

The properties of the backing sheet produced as described above aretypically: tensile strength at break--5.35 kg/mm² ; elongation atbreak--990%; thickness--0.002 inches; MVTR--8,100 g/m² /24 hrs.

EXAMPLE 4 Assembly of Wound Dressing

To construct the absorbent wound dressing, the respective sheets andlayers produced in accordance with Examples 1-3, above, are assembled asfollows:

The polyurethane backing is coated with a thin layer of an aproticsolvent such as dimethylacetamide (DMAC), dimethylformamide (DMF) ordimethylsulphoxide (DMSO). The solvent of choice is DMSO. Alternatively,a thin layer of the hydrophilic polyurethane dissolved in a solvent canbe utilized as an adhesive. The backing is placed onto the surface faceof the porous polyurethane sheet free from macropores. Pressure isapplied to the composite to minimize air entrapment at the interface.The resulting structure is placed in a forced hot air oven for about 25to about 35 minutes at about 65° to about 75° C. This heat treatmentremoves any bonding solvent that may be present.

Subsequently, the macropore-containing face of the porous layer iscontacted with the preformed pressure sensitive adhesive layer. Bondingis achieved by applying heat and/or pressure to the resulting composite.

The sheet-form composite is then subjected to a compressive force toform apertures in the adhesive layer.

The completed sheet-form composite is cut to the desired size and shape,packaged in medical heat sealable pouches and sterilized.

This sheet-form composite embodying the present invention has thefollowing physical characteristics: tensile strength to break--0.18kg/mm² ; elongation at break--630%; thickness--0.026 inches; waterabsorption--225%; MVTR--6,900 g/m² /24 hrs.

EXAMPLE 5 Manufacture of Wound Dressing Without Backing

The porous layer and the adhesive layer are formed as disclosed inExamples 1 and 2, above. The porous layer and the adhesive layer arethen bonded together and further processing is done as described inExample 4, above.

This produced sheet-form material has the following properties: tensilestrength to break--0.09 kg/mm² ; elongation at break--326%; thickness--0.03 inches; water absorption--500%; MVTR--24,000 g/m² /24 hrs.

EXAMPLE 6 Manufacture of Wound Dressing Without Backing

The porous layer of this example is fabricated from Mitrathane™ M2007, asegmented polyetherurethane-urea. The material is supplied as a 25weight percent solids solution in dimethylacetamide (DMAC). To thisMitrathane™ solution a solution of polyvinylpyrollidone (PVP; M.W.360,000) in DMAC is added such that the total solids of the mixture is17 weight percent in DMAC (15% Mitrathane™ M2007, 3% PVP). The resultingpolymer solution is then processed as described in Example 1, above,into a porous sheet. A wound dressing is then fabricated as described inExample 5, above.

The resulting sheet-form material has the following physicalcharacteristics: tensile strength to break--0.17 kg/mm² ; elongation atbreak--500%; thickness--0.02 inches; water absorption--190%; MVTR--9,800g/m² /24 hrs.

EXAMPLE 7 Manufacture of Wound Dressing Without Backing

The porous layer is made from Mitrathane™ M2007, apolyetherurethane-urea by the process described in Example 1, above. Awound dressing is then fabricated as described in Example 5, above.

The resulting wound dressing has the following physical characteristics:tensile strength to break--0.32 kg/mm² ; elongation at break--450%;thickness--0.017 inches; water absorption--250%; MVTR--1,370 g/m² /24hrs.

This invention has been described in terms of specific embodiments thathave been set forth in detail. It should be understood however, thatthese embodiments are by way of illustration only and that the inventionis not necessarily limited thereto. Modifications and variations will beapparent from this disclosure and may be resorted to without departingfrom the spirit of this invention, as those skilled in the art willreadily understand. Accordingly, such variations and modifications ofthe disclosed products are considered to be within the purview and scopeof this invention and the following claims.

We claim:
 1. A process for manufacturing an adhesive-faced, sheet-formabsorbent material suitable as a wound or burn dressing, surgical drapeor the like wherein said adhesive facing is apertured, which processcomprises the following steps:providing an elastomeric, absorbent,porous sheet said porous sheet having an open pore structure anddefining macropores on one surface of said macroporous sheet; providingan adhesive layer as a viscous mass on a release surface said adhesivelayer having a cohesive strength less than the adhesive strength of theadhesive to the porous sheet; juxtaposing said porous sheet and saidadhesive layer such that said adhesive layer is contiguous with themacropore-containing surface of said porous sheet; compressing saidjuxtaposed porous sheet and adhesive layer; and removing said appliedcompressive force from a resulting laminate so that when said poroussheet springs back to its previous configuration portions of theadhesive layer bond to at least some of the surfaces of the macroporesof the porous sheet forming apertures in said adhesive layer.
 2. Theprocess of claim 1 further comprising the step of securing a liquidimpermeable but water vapor permeable backing sheet to the sheet-formabsorbent material.
 3. The process of claim 1 wherein said porous sheetis a segmented polyurethane.